The present invention relates to solvent-free water-based emulsions of anionically polymerizable polymers. Specifically, the invention relates to solvent-free water-based emulsions of hydrogenated butadiene diols, epoxidized diene polymers and acrylic monomer-containing block copolymers.
Anionically polymerized polymers are well known. Polymers such as polystyrene, polybutadiene, polyisoprene, styrene/butadiene rubber, block copolymers of vinyl aromatic hydrocarbons and conjugated dienes, etc. exhibit excellent properties and have a wide variety of uses including coatings and adhesives. However, such polymers are not water soluble and this lack of solubility in water limits their usefulness in efforts to replace solvent based adhesive, sealants, and coatings with equivalent water-based systems.
Water-based dispersions of such polymers can easily be prepared by diluting the polymers with solvent, emulsifying the low viscosity organic phase into an aqueous surfactant solution with a high shear mixer and stripping off the solvent. Such dispersions are quite useful but they suffer from the disadvantage that a solvent must be used in preparation and thus must be disposed of, increasing the cost and environmental hazards. It would be highly advantageous to be able to produce films from water-based emulsions of polymers which have the properties of films produced by hot melt or solvent casting with the above anionically polymerized polymers without the necessity of incorporating a solvent in the preparation of the dispersion. Such emulsions or dispersions would have very low viscosity even with high molecular weight polymers and could be applied as formulated coatings or adhesives in a solvent-free system. Optionally, small amounts of organic solvent could be added to these systems as coalescing aids.
U.S. Pat. No. 4,239,672 describes a method for emulsifying low molecular weight polybutadienes which have been maleated or epoxidized. Example 5 describes the emulsification of a very low molecular weight liquid polybutadiene having a viscosity of 30 cp. This emulsification was carried out without the use of any solvent. Other examples in the patent describe the emulsification of a liquid butadiene homopolymer with a viscosity of 750 cp. In each of these examples, a significant amount of solvent was used. The first polybutadiene had a viscosity low enough to allow it to be emulsified with stirring used as the mixing technique, a rather low intensity mixing technique. The higher viscosity polymer required solvent to allow it to be emulsified using the same low intensity mixing technique.